This invention relates to input and output devices, in particular a stage of both input and output which may be configured to operate with low and high voltages.
It is well recognized that standard input and output stages have some limitations to their operation which are mainly brought about by the technologies employed in their making.
Specifically, the input and output stages are implemented in technologies which forbid implementation on the same chip of circuit portions which operate with low voltages and circuit portions which operate with high voltages.
The technical problem underlining the present invention is that of realizing a mixed technology stage of both input and output which may be configured to operate with low and high voltages.
In fact, by using a mixed technology, both low and high voltage circuit portions can be implemented on one chip.
The above technical problem is solved by a stage of both input and output in which--in addition to a DMOS pull-down device and a PMOS pull-up device--an additional DMOS device is interposed between the output node and the pull-up device. By turning on the additional DMOS device, the stage can be operated as a push-pull output; by turning off the additional DMOS device, the stage can be operated as an open-collector stage (with the intrinsic diode of the additional DMOS device providing protection for the pull-up device).